The field of the present invention relates to building materials and particularly to “green” building blocks made from culm such as residual rice straw, a by-product of the rice growing industry.
Providing affordable housing while decreasing air pollution is an ideal worth fighting for. Housing is typically considered by most not to be affordable due, in part, to the high cost of the building materials. Conventional building materials, such as lumber, are costly because they are becoming more and more scarce as the demand for more and more housing increases to meet the needs of the world's burgeoning population. In addition, when the trees are cut down to make the lumber to build the house, the result is an adverse effect on our air quality as these natural resources are no longer able to turn carbon dioxide into oxygen.
In an effort to find alternative building materials, people have been turning to recycled goods and/or the by-products of an industry. One such source has been culm, commonly referred to as straw, which is what is left over when grains, such as wheat, rice, barley, oats, and rye, are harvested. Straw is a viable building material because it is plentiful and inexpensive. Buildings built with straw bales have well-insulated walls, simple construction, and low costs. Moreover, in many areas, straw is still burned in fields, producing significant air pollution. For example, in California more than one million tons of rice straw were burned each fall in the early 1990's, generating an estimated 56,000 tons of carbon monoxide annually, which is approximately twice that produced from all of the state's power plants. By converting an agricultural by-product into a valued building material, another benefit to the community is therefore a reduction in air pollution.
A number of drawbacks exist to the use of straw as a building material. Straw does not have the same structural integrity as wood, cement, or other conventional building materials. As a consequence, straw does not have the load bearing capacity that so many architects, engineers, and contractors require. Straw is also highly susceptible to moisture and can and will rot if there is too much exposure to moisture over time. Moreover, straw bales are of an inconsistent quality. They are also not sized to building industry standards.
FIG. 5 is illustrative of some of these points. Shown there are two differently sized conventional straw bales, namely, a 3-tie straw bale on the left and a 2-tie straw bale on the right. The denomination of “3-tie” or “2-tie” is due to the number of ties T being wrapped about the straw stalks S, as seen in FIG. 5. The larger 3-tie bale is typically 32″ to 47″ long by 23″ to 24″ wide by 14″ to 17″ high. The dimensions of a 2-tie bale are similarly varied and are typically in the range of 35″ to 40″ long by 18″ wide by 14″ high. A conventional concrete or cinder building block, however, is typically 24″ long by 12″ wide by 12″ high. The weight of a 3-tie bal can be anywhere between 75 to 100 lbs., whereas a 2-tie bale is typically 50 lbs. OSHA product weight requirements, however, require less than 50 lbs. per block, with 40 lbs. typically being an acceptable weight that can be handled by one person.
FIG. 5 illustrates that the straw stalks S of a conventional straw bale appear to be aligned parallel to a single axis of alignment, Aw. The appearance of alignment occurs because of the cut, rake, and bale process of making the bale. There are no machines or modifications of machines that intentionally align the straw to make specific straw-aligned bales. The general alignment Aw of the straw S can be described as “horizontally aligned”, i.e., horizontal or parallel to the ground G when the bale is laid flat. The general alignment Aw can also be described as running parallel to the width W axis and perpendicular to the length L and height H axes or, alternatively, parallel to the plane defined by the top or bottom walls (the intersection of the L and W axes).
It is the inventors' understanding that those skilled in the art prefer “horizontal alignment” to increase the load bearing capacity of each bale. Gleaned from compression tests of individual bales, the prior art teaches that flat bales can carry far more load than bales stacked on edge. Flat bales failed at an average load of 10,000 lb/ft2 (48,800 kg/m2); on edge, bales failed at an average of 2,770 lb/ft2 (13,500 kg/m2). To further increase the load bearing capacity of the bale other than laying it flat, the prior art also teaches the use of threaded rods that may be inserted through each bale or framed around each bale and then bolted through a wide top plate and tightened down after the roof is installed. Pre-compressing the walls in this manner minimizes further settling after the roof is installed.
FIG. 5 also illustrates how conventional prior art straw bales do not have a smooth cut surface and the corners are rounded, i.e., the edges are not crisp and the corners are not square. What FIG. 5 does not illustrate is the high level of susceptibility to moisture damage that straw has or the inconsistent and often poor quality of the traditional straw bale itself.
A “green” building material such as a culm or straw block that has an increased load bearing capacity over traditional straw bales, is of a consistent quality, is sized for building industry standards, and has an increased resistance to water damage is therefore desired.